Method and apparatus for improving turbocharger components

ABSTRACT

In one form, a turbocharger component, such as a compressor wheel or an impeller, formed of a cast material or a material made using a powder metal process, includes a surface having at least a portion thereof treated by a thermo-mechanical treatment process, such as friction stir processing. At the treated portion, the material forming the component includes a microstructure that is different than the microstructure of the material throughout the rest of the component. For example, in one form the material at the treated portion includes a homogenous microstructure while the material throughout the rest of the component includes a cast microstructure. In one or more forms, the treated portion exhibits at least one of increased strength, ductility and fatigue-resistant properties. In another form, a method is directed to providing components for a turbocharger which exhibit enhanced structural properties. However, other embodiments, forms and applications are also envisioned.

BACKGROUND

The present application relates to turbochargers for internal combustion engines, and more particularly, but not exclusively, relates to one or more components of the turbocharger having one or more improved structural properties.

Turbochargers are well known devices for pressurizing intake air entering the combustion chambers of an internal combustion engine to thereby increase the efficiency and power output of the engine. Generally, pressurizing the intake air increases the quantity of air entering the engine combustion chambers during intake, permitting more fuel to be utilized in establishing a fuel charge with a desired air-to-fuel ratio. Typically, increased engine torque and power results compared to a similar engine that is not turbocharged.

In a turbocharged engine, the exhaust manifold of the engine is in fluid communication with a rotatable turbine of the turbocharger via an exhaust conduit, and the exhaust gas flowing through this conduit causes the turbine to turn at a rate determined by exhaust gas pressure and flow rate. A compressor of the turbocharger is mechanically coupled to the turbine. The compressor is rotatably driven by the turbine as it turns. An inlet of the compressor receives fresh ambient air, and an outlet of the compressor is in fluid communication with an intake manifold of the engine via an intake conduit. The rotation of the compressor increases the amount of intake air supplied to the engine, which results in an increased pressure, often referred to as the “boost” pressure.

Various components typically found in a turbocharger for an internal combustion engine are susceptible to mechanical fatigue failure due to high-amplitude, cyclic loading. In one particular example, a component such as a compressor wheel or impeller manufactured from an aluminum or aluminum alloy casting suffers fatigue failure at surface defects which are exposed as the component is machined to finished dimensions. In another example, a component such as a compressor wheel or impeller manufactured using a powder metal process can suffer fatigue failure at surface defects resulting from the manufacturing process. In yet another example, the casting includes defects in the form of one or more voids, dendrites, microstructural segregation and inclusions, each of which acts as a stress concentrator leading to early fatigue failure. Often times, these defects will lie in highly stressed regions, such as the surface positioned opposite a plurality of vanes of the compressor wheel or impeller. Fatigue failure of these components often leads to extensive damage to surrounding opponents and usually results in costly and lengthy repairs. Current approaches to address fatigue failure in these components tend to be expensive, limit manufacturing and design flexibility and/or increase waste of raw materials.

Thus, there is a need for additional contributions in this area of technology.

One nonlimiting embodiment of the present application is directed to a cast turbocharger component, such as a compressor wheel or an impeller, which includes a surface having at least a portion thereof treated by a thermo-mechanical treatment process, such as friction stir processing. The material of the component at the treated portion includes a microstructure that is different than the microstructure of the material at one or more other locations in the component or possibly throughout the rest of the component. In one or more forms, the treated portion exhibits at least one of increased strength, ductility and fatigue-resistant properties, thereby improving the overall structural properties of the component. However, in other embodiments, different forms and applications are envisioned.

Another embodiment of the present application is a unique component for use in a turbocharger of an internal combustion engine. Other embodiments include unique methods, systems, devices, kits, assemblies, equipment, and/or apparatus involving a turbocharger component having one or more improved structural properties.

Further embodiments, forms, features, aspects, benefits, objects and advantages of the present application shall become apparent from the detailed description and figures provided herewith.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a vehicle including an internal combustion engine system.

FIG. 2 is a diagrammatic illustration of the internal combustion engine system illustrated in FIG. 1.

FIG. 3 is a cross-sectional view of a turbocharger of the engine system of FIGS. 1 and 2.

FIG. 4 is an enlarged perspective view of the compressor wheel of the turbocharger illustrated in FIG. 3.

FIG. 5 is a macrograph illustrating the microstructure of the material forming a cast component of the turbocharger in FIG. 3.

FIGS. 6 a-6 d illustrate the application of a thermo-mechanical treatment process to a surface of the compressor wheel illustrated in FIG. 4.

FIG. 7 is a macrograph illustrating a refined, homogenous microstructure of the material illustrated in FIG. 5.

FIG. 8 is a macrograph illustrating a stir zone in a portion of a component treated with friction stir processing.

DETAILED DESCRIPTION OF REPRESENTATIVE EMBODIMENTS

While the present application can take many different forms, for the purpose of promoting an understanding of the principles of the application, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the application is thereby intended. Any alterations and further modifications of the described embodiments, and any further applications of the principles of the application as described herein are contemplated as would normally occur to one skilled in the art to which the application relates.

One embodiment of the present application is directed to a cast component of a turbocharger which includes a surface having at least a portion thereof treated by a thermo-mechanical treatment process, such as friction stir processing, further details of which are provided below. As used herein, the term “cast” is used to describe a component formed from a material which has been poured or forced into a mold in a liquid or molten state, allowed to harden in the mold and subsequently removed from the mold. As would be appreciated by those skilled in the art, the shape of the component when removed from the mold will be the same as or substantially similar to its final shape. However, it is contemplated that the component may further undergo additional processing, such as machining for example, to achieve its final shape. In one embodiment, the cast component may be formed through one of sand casting, plaster casting, shell molding, investment casting, die casting, centrifugal casting and continuous casting, just to name a few possibilities.

Another embodiment of the present application is directed to a component of a turbocharger made using a powder metal process which includes a surface having at least a portion thereof treated by a thermo-mechanical treatment process, such as friction stir processing. For the sake of clarity in describing and claiming the subject matter of the present application, various features and embodiments are described below in the context of a cast component; however, the materials described in the following description are equally applicable to treatment of a component made using a powder metal process. As such, in the present specification, use of the term “cast component” is intended to apply equally to a component made using a powder metal process. Similarly, use of the term “cast microstructure” is intended to apply equally to a microstructure produced by powder metal processing, referred to herein as “powder metal microstructure”; use of the term “casting porosity” is intended to apply equally to porosity of a material produced by powder metal processing, referred to herein as “powder metal porosity”; and use of the term “casting defects” is intended to apply equally to defects in a material produced by powder metal processing, referred to herein as “powder metal defects.”

It is contemplated that the cast component may be formed of any metal or metal alloy amenable to use in the casting process or powder metal process. Various examples of metals and metal alloys include, without limitation, carbon steel, zinc, zinc alloys, copper, copper alloys, nickel, nickel alloys aluminum and aluminum alloys. In a particular form, the cast component is formed of aluminum or an aluminum alloy. The aluminum alloy may be, for example, a mixture of aluminum with one or more of copper, silicon, magnesium, zinc, nickel and tin.

As will be explained in further detail with respect to FIGS. 1-4, a turbocharger for an internal combustion engine system includes several components, any one or more of which may be cast and treated with the thermo-mechanical process discussed herein. As way of background, FIG. 1 illustrates a side view of vehicle 10 powered by an internal combustion engine system 11. Vehicle 10 could be a variety of types of vehicles, for example, a light duty truck, a medium duty truck, a heavy duty truck, a passenger vehicle, a bus, or an industrial or construction vehicle. In a non-illustrated form, engine system 11 may provide power to other equipment or mechanical devices, such as generators, pumps, air compressors, farm equipment, construction equipment, automobiles and other vehicles, just to name a few possibilities. Engine system 11 includes an engine 12, which in one form is a diesel engine but could be other types of internal combustion engines, and a turbocharger 13.

Referring now to FIG. 2, further details of engine system 11 are diagrammatically illustrated. Turbocharger 13 includes a compressor 14 and a turbine 16. Engine 12 includes intake manifold 48 fluidly coupled to compressed air outlet 44 of compressor 14 via compressed air conduit 50. Compressor 14 includes ambient air inlet 42 coupled to intake conduit 52 for receiving fresh air therefrom. Optionally, an intake air cooler of known construction can be disposed in-line with compressed air conduit 50 between compressor 14 and intake manifold 48 (not shown). Compressor 14 is mechanically coupled to turbine 16 via drive coupling 32, wherein turbine 16 includes exhaust gas inlet 36 fluidly coupled to exhaust manifold 54 of engine 12 via exhaust conduit 56, and further includes exhaust gas outlet 38 fluidly coupled to ambient air via exhaust conduit 58. Exhaust Gas Recirculation (EGR) valve 60 is disposed in line with EGR conduit 62. EGR conduit 62 is in fluid communication with compressed air conduit 50 and exhaust conduit 56. Optionally, an EGR cooler of known construction can be disposed in-line with EGR conduit 62 between EGR valve 60 and compressed air conduit 50 (not shown).

In one form, engine 12 is of a conventional, four-stroke, reciprocating piston variety. However, in lieu of a reciprocating piston-based engine, a rotor-based engine may be utilized in an alternative embodiment of the present application. Also, in other embodiments, an engine with a different number of operating cycles, such as a two-cycle sequence, may be utilized. Coupling 32 may be in the form of a rotatable drive shaft, pulley and belt arrangement, intermeshing gears, a combination of these, and/or such other arrangement to drive compressor 14 with turbine 16 as would occur to those skilled in the art. In still other embodiments, multistage compressors, multistage turbines, or a combination of these are envisioned.

Engine system 11 includes controller 70 that is preferably microprocessor-based and is generally operable to control and manage the overall operation of engine 12. Controller 70 includes memory 72 as well as a number of inputs and outputs (not shown) for interfacing with various sensors and systems coupled to engine 12. Controller 70 can be provided in the form of one or more components based on digital circuitry, analog circuitry, or a combination of these; and/or can be based on one or more central processing units (CPUs), arithmetic logic units (ALUs), or the like; of a RISC, CISC, or any other variety. For a multiple component form, such components can be integrated in a single unit or remotely located relative to one another. Controller 70, in one embodiment, may be a known control unit sometimes referred to as an electronic or engine control module (ECM), electronic or engine control unit (ECU) or the like. Controller 70 includes desired support components, such as a power supply, signal conditioners, filters, limiters, format converters (such as analog-to-digital and/or digital-to-analog types), input/output controllers, communications ports, operator input/output devices, and the like as would occur to those skilled in the art. Memory 72 can be comprised of one or more types, including, but not limited to electronic, optical, and/or electromagnetic varieties and/or can be volatile, nonvolatile, or a combination of these.

Controller 70 preferably executes operating logic to perform one or more control routines. Such logic can be in the form of software or firmware programming instructions, dedicated hardware (such as a synchronous state machine or asynchronous machine), one or more signals encoded to provide controller instructions and/or direct controller operation, or a combination of these, to name just a few examples.

Further details of turbocharger 13 are illustrated in section view in FIG. 3. Turbocharger 13 includes a central bearing housing 18 positioned between compressor 14 and turbine 16. Turbine 16 comprises a turbine housing 19 which houses a turbine wheel 20. Similarly, compressor 14 comprises a compressor housing 22 which houses a compressor wheel 24. It should be appreciated that, the terms “compressor wheel” and “impeller” are interchangeably used herein to describe component 24. Compressor wheel 24 generally includes a body 25 extending between a first surface 26 facing turbine wheel 20 and a second surface 28 facing ambient air inlet 42. As illustrated in an enlarged perspective view in FIG. 4, surface 28 of compressor wheel 24 includes a plurality of vanes 30. Drive coupling 32 to which turbine wheel 20 and compressor wheel 24 are mounted is supported on bearing assemblies 34 within bearing housing 18.

Turbine housing 18 is provided with exhaust gas inlet 36 and exhaust gas outlet 38. Exhaust gas inlet 36 directs incoming exhaust gas to an annular inlet chamber 40 which forms a volute surrounding the turbine wheel 20. The exhaust gas flows through the turbine and into the exhaust gas outlet 38 via a circular outlet opening which is coaxial with the turbine wheel 20. Compressor housing 22 is provided with ambient air inlet 42 and compressed air outlet 44. The ambient air flows through ambient air inlet 42, is compressed by compressor wheel 24 and forced toward compressed air outlet 44 through outlet chamber 46 which forms a volute surrounding compressor wheel 24.

As indicated above, one or more of the components of turbocharger 13 may be cast and include a surface with at least a portion treated with the thermo-mechanical treatment process described herein. In one form, the cast component is one or both of compressor wheel 24 and turbine wheel 20. In another particular form, the cast component is compressor wheel 24. Regardless of the identity of the component, it should be appreciated that any surface thereof, in whole or in part, may be treated with the thermo-mechanical treatment process. For example, where the component is compressor wheel 24, the treated surface may include at least a portion of one or both of first surface 26 and second surface 28. In one particular form, all or part of first surface 26 is treated with the thermo-mechanical treatment process.

In FIG. 5 there is provided a macrograph 80 representative of the microstructure of an aluminum or aluminum alloy material 82 cast to form one or more of the components of turbocharger 13, such as compressor wheel 24. More particularly, macrograph 80 illustrates that material 82 includes casting porosity 84 and a dendritic microstructure. Material 82 may also include other casting defects, such as voids, dendrites, microstructural segregation and inclusions. In order to remove the casting porosity and defects and refine the microstructure of the material and thereby provide a component with enhanced structural properties, the component is treated with a thermo-mechanical treatment process, such as friction stir processing, further details of which are provided below.

Referring now to FIGS. 6 a-6 d, there is illustrated a friction stir processing treatment being applied to a surface of compressor wheel 24. It should be appreciated that the friction stir processing treatment described herein may also be applied to other components of turbocharger 13, including for example, turbine wheel 20. Additionally, while FIGS. 6 a-6 d illustrate the friction stir processing treatment being applied to surface 26 of compressor wheel 24, it is contemplated that one or more different surfaces of compressor wheel 24 may be treated in addition to or in lieu of surface 26. FIG. 6 a illustrates step 100 of the friction stir processing treatment which is applied with an elongated machining tool 102. Tool 102 includes a distal pin 104 extending from an enlarged portion 106 which defines a shoulder 108 concentrically positioned relative to pin 102. In step 100, tool 102 is rotated about its longitudinal axis L, as indicated by arrow R. As tool 102 is rotated, it is moved toward surface 26 of compressor wheel 24 as indicated by directional arrow D to bring pin 104 into contact with surface 26, as illustrated in FIG. 6 b. As pin 104 initiates contact with surface 26, it heats and softens a small column of material 82 and creates a stir zone 112. It should be appreciated that the insertion depth of tool 102 into surface 26 is controlled by shoulder 108 and the length of pin 104.

In step 120 illustrated in FIG. 6 c, tool 102 is moved in the direction of arrow D until shoulder 108 contacts surface 26. Shoulder 108 adds additional heat to surface 26 and a larger column of material 82 is plasticized around pin 104. Rotating shoulder 108 also provides a forging force which contains the upward flow of the plasticized material caused by pin 104. In step 130 illustrated in FIG. 6 d, one or both of tool 102 and surface 26 of compressor wheel 24 is moved transversely to the other and the size of stir zone 112 is increased. As stir zone 112 increases, plasticized material from the leading edge of pin 104 is transported to the trailing edge of pin 104 and defects in the material of stir zone 112 are removed. After being treated by tool 102, material 82 in stir zone 112 cools without solidification and forms a microstructure exhibiting a refined grain structure. It should be appreciated that the process described with respect to FIGS. 6 a-6 d may be continued until the desired area of surface 26 is treated.

While not being limited to any single form, it is contemplated that, after grain refinement by treatment with tool 102, material 82 of stir zone 112 may include one or more of a lamellar or banded, fine grain, or Widmanstaten or basket weave microstructure. In another form, material 82 at stir zone 112 exhibits a refined grain size microstructure, which may, for example, be similar to a forged microstructure, but having smaller grains. In this regard, treatment of material 82 in stir zone 112 with tool 102 can be described as being equivalent of localized forging and grain refining. In yet another form, material 82 at stir zone 112 generally includes a homogenous microstructure. In another more particular form, as illustrated by macrograph 140 of FIG. 7, material 82 at stir zone 112 includes a fine grained homogenous microstructure, with all or substantially all of the casting defects being removed therefrom. In still another form, one or more of the casting defects is removed at stir zone 112. It should be appreciated that the final microstructure may be at least partially dependent on the constituent metal or metals of material 82.

Referring now to FIG. 8, macrograph 150 provides further details with respect to one representative stir zone 112 of surface 26 treated by friction stir processing. Material 82 at stir zone 112 includes a homogenous microstructure. However, material 82 underlying and outlying stir zone 112 still includes the original or cast microstructure, including casting porosity and other casting defects. As illustrated, there is a gradual transition between the microstructure of material 82 at stir zone 112 and the cast microstructure of surrounding material 82. Additionally, it is contemplated that stir zone 112 may extend to a depth of from about 0.5 mm to about 150 mm or more below surface 26. In one embodiment, stir zone 112 extends to a depth of from about 0.5 mm to about 100 mm. In another embodiment, stir zone 112 extends to a depth of from about 0.5 mm to about 50 mm.

The subject application contemplates that material 82 having a refined grain structure at stir zone 112 by treatment with tool 102 may exhibit one or more of increased yield strength, tensile strength, ductility, formability and resistance to fatigue and corrosion. It is also contemplated that material 82 at stir zone 112 may exhibit superplasticity. While enhancing the properties of material 82 at stir zone 1 12, refining the microstructure at this area may also impart enhanced structural properties to compressor wheel 26 as a whole. For example, removing casting defects, which often make the entire compressor wheel 24 susceptible to fatigue failure, may increase the fatigue-resistance and/or life of compressor wheel 24. While not illustrated in FIGS. 6 a-6 d, the friction stir processing treatment described herein may optionally be used to incorporate alloying materials into the layers of material 82 near surface 26. For example, alloying materials can be provided in the form of thin sheets, wire, powder, or other forms as would occur to a person of ordinary skill in the art. The present application also contemplates embodiments in which friction stir processing treatment is used to incorporate alloying materials into the surface of a turbocharger component that is formed using other manufacturing process, such as, for example, and without limitation, machining from bar stock or forged material. Furthermore, the present application contemplates that one or more variations may be made to the friction stir processing treatment described herein as would be appreciated by those skilled in the art. For example, and without limitation, the present application contemplates the use of laser-assisted friction stir processing treatment.

Another embodiment of the application is directed to a method including providing a cast component of a turbocharger for an internal combustion engine. The component is formed of a material including a cast microstructure. The method also includes applying a friction stir processing treatment to at least a portion of a surface of the component and thereby altering the cast microstructure of the material at the portion. In one form, the providing includes inspecting a preassembled turbocharger for defects and removing a cast component from the turbocharger as a result of detecting at least one defect therein. As a further variant of this form, applying the thermo-mechanical process is limited to treating the portions of the component including the detected defects. The method may also include reassembling the turbocharger with the cast component after application of the thermo-mechanical treatment process. In still a further form, the applying includes at least one of refining a grain structure of the cast microstructure, homogenizing the cast microstructure and removing casting defects from the cast microstructure at the portion.

Yet another embodiment of the present application includes a method including providing a cast component of a turbocharger. The method also includes identifying at least one highly stressed area on a surface of the cast component and applying a friction stir processing treatment to at least one of the highly stressed areas of the surface. In one form, the thermo-mechanical treatment process includes friction stir processing.

A further embodiment includes a method for manufacturing a cast component of a turbocharger including: pouring or forcing a liquid or molten metal or metal alloy material into a mold; allowing the material to cool and harden in the mold; removing the hardened material from the mold; and applying a friction stir processing treatment to at least a portion of a surface of the cast component. In one form, the method may also include machining the component to its final form after removing it from the mold. In a further form, the method also includes assembling a turbocharger to include the component treated by the friction stir processing.

Still a further embodiment comprises a turbocharger including a compressor wheel coupled with a first end of a shaft and a turbine coupled with an opposite second end of the shaft. The compressor wheel includes a surface facing the turbine and includes at least a portion of the turbine-facing surface treated by a thermo-mechanical treatment process. The compressor wheel is formed of a material including a first microstructure and a second microstructure, where the second microstructure is limited to the portion treated by the thermo-mechanical treatment process. In one form, the thermo-mechanical treatment process includes friction stir processing. In another particular form, the first microstructure is a cast microstructure including at least one of casting defects, segregated chemistries and an inhomogenous microstructure and the second microstructure is a homogenous microsctructure being substantially free from casting defects.

Yet a further embodiment comprises a cast impeller for a turbocharger compressor, including a body having a cast micristructure extending between a first surface and a second surface. At least one of the first and second surfaces includes at least a portion thereof treated by a friction stir processing treatment and having a second microstructure exhibiting at least one of increased strength, ductility and fatigue-resistant properties relative to the cast microstructure. In one form, the first surface includes a plurality of vanes and the second surface includes the portion treated by the friction stir processing treatment. In another form, the impellor is formed of aluminum or an aluminum alloy.

Still, other embodiments of the application include providing a turbocharger component having enhanced structural properties. In one embodiment, the turbocharger is a compressor wheel or impellor formed of aluminum or an aluminum alloy.

Any theory, mechanism of operation, proof, or finding stated herein is meant to further enhance understanding of the present application and is not intended to make the present application in any way dependent upon such theory, mechanism of operation, proof, or finding. It should be understood that while the use of the word preferable, preferably or preferred in the description above indicates that the feature so described may be more desirable, it nonetheless may not be necessary and embodiments lacking the same may be contemplated as within the scope of the application, that scope being defined by the claims that follow. In reading the claims it is intended that when words such as “a,” “an,” “at least one,” “at least a portion” are used there is no intention to limit the claim to only one item unless specifically stated to the contrary in the claim. Further, when the language “at least a portion” and/or “a portion” is used the item may include a portion and/or the entire item unless specifically stated to the contrary. While the application has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the selected embodiments have been shown and described and that all changes, modifications and equivalents that come within the spirit of the application as defined herein or by any of the following claims are desired to be protected. 

1. An apparatus, comprising: a turbocharger for an internal combustion engine, said turbocharger including a compressor wheel coupled with a first end of a shaft and a turbine coupled with an opposite second end of said shaft, said compressor wheel including a first surface facing said turbine and a second surface including a plurality of vanes and facing away from said turbine; wherein said compressor wheel comprises a material having a first microstructure; and wherein at least a portion of said first surface comprises a second microstructure, said second microstructure being formed by a localized friction stir processing treatment.
 2. The apparatus of claim 1, wherein said compressor wheel is formed of a material selected from the group consisting of a cast material and a material made using a powder metal process.
 3. The apparatus of claim 2, wherein said second microstructure comprises a homogenized microstructure containing a reduced number of casting defects relative to said first microstructure.
 4. The apparatus of claim 1, wherein: said portion includes a stir zone defined by said friction stir processing; said stir zone comprises said second microstructure; said first microstructure of the material lies beneath said stir zone; and said material includes a gradual transition between said stir zone and said first microstructure.
 5. The apparatus of claim 1, wherein said material is selected from the group consisting of aluminum and aluminum alloys.
 6. The apparatus of claim 1, wherein at least a portion of said first surface comprising said second microstructure includes an alloying material incorporated therein by said localized friction stir processing treatment.
 7. A method, comprising: providing a cast component of a turbocharger for an internal combustion engine, said component comprising a material including a cast microstructure; and applying a friction stir processing treatment to at least a portion of a surface of said component and thereby altering the cast microstructure of the material at said portion.
 8. The method of claim 7, wherein said cast component is selected from the group consisting of a turbine wheel and a compressor wheel.
 9. The method of claim 7, wherein said component is a compressor wheel including a plurality of vanes and said surface is positioned opposite said plurality of vanes.
 10. The method of claim 9, wherein the material is selected from the group consisting of aluminum and aluminum alloys.
 11. The method of claim 7, wherein: treating said portion with said friction stir processing treatment defines a stir zone at said portion; said cast microstructure lies beneath said stir zone; and the material includes a gradual transition between said stir zone and said cast microstructure.
 12. The method of claim 11, wherein said stir zone extends from said surface to a depth of from about 0.5 mm to about 150 mm.
 13. The method of claim 7, wherein said applying said friction stir processing comprises incorporating an alloying material into the stir zone.
 14. The method of claim 13, wherein said alloying material comprises a form selected from the group consisting of a thin sheet, a wire and a powder.
 15. The method of claim 7, wherein altering the cast microstructure of the material at said portion includes at least one of homogenizing the cast microstructure, removing casting defects from the cast microstructure at said portion and incorporating an alloying material into said portion.
 16. The method of claim 15, wherein removing casting defects includes substantially eliminating at least one of voids, dendrites, microstructural segregation and inclusions from the material at said portion.
 17. The method of claim 7, wherein said providing includes inspecting a preassembled turbocharger for defects and removing a cast component from said preassembled turbocharger as a result of detecting at least one defect in said cast component.
 18. The method of claim 7, further comprising identifying at least one highly stressed area of said cast component and wherein said applying said friction stir processing treatment comprises applying said friction stir processing treatment to at least one of said at least one highly stressed areas of said cast component.
 19. A cast impeller for a turbocharger compressor, comprising a body having a cast microstructure extending between a first surface and a second surface, wherein at least one of said first and second surfaces includes at least a portion treated by a friction stir processing treatment and having a second microstructure exhibiting at least one of increased strength, ductility and fatigue-resistant properties relative to the cast microstructure.
 20. The impeller of claim 19, wherein said first surface includes a plurality of vanes and said second surface includes said portion.
 21. The impeller of claim 19, wherein said body comprises a material selected from the group consisting of aluminum and aluminum alloys. 